[INTERNAL] cleaned up EditorManager

Removed dead code, made all protected methods and fields either private
or package protected. Move classes temporarily from the internal package
to editor package so they could access the package protected methods and
fields.

Also added FIXMEs.

Change-Id: Ie05d850e3bf9ff637fb041b09b18b0cae67df63b
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/1741
Tested-by: Saros-Eclipse QA
Tested-by: Jenkins CI
Reviewed-by: Stefan Rossbach <srossbach@arcor.de>